1. FIELD OF THE INVENTION
This invention relates to a signal processing method in autoradiography.
2. DESCRIPTION OF THE PRIOR ART
Autoradiography has been known as a method for obtaining locational information on radioactively labeled substances distributed in at least one dimensional direction to form distributed rows on a support medium.
For instance, the autoradiography comprises steps of: labeling organism-originating biopolymers such as proteins or nucleic acids with a radioactive element; resolving the radioactively labeled biopolymers, derivatives thereof, or cleavage products thereof on a gel support (support medium) through a resolving process such as gel electrophoresis; placing the gel support and a high-sensitivity type X-ray film together in layers for a certain period of time to expose said film, developing said film, obtaining the location information of the radioactively labeled substances from the developed film, and then performing the identification of the polymeric substances, determination of molecular weight thereof and isolation thereof based on the obtained locational information.
Autoradiography has a prominent advantage in that visual observation of the locational information in a cell scale or a molecular scale on radioactively labeled substances can be made by utilizing the radiography as mentioned above. However, in other words, it is essential in conventional radiography to visualize the autoradiograph having the locational information on a radiographic film in order to obtain the locational information on the radioactively labeled substances.
In fact, investigators have determined the distribution of radioactively labeled substances in a sample by observing a visualized autoradiograph with their eyes to obtain the locational information on the specific substances labeled with a radioactive element.
The certain locational information as obtained above has been further subjected to various analyses to isolate or identify radioactively labeled substances, or to determine the molecular weight or characteristics of specific substances. For instance, the above-mentioned autoradiography is used effectively to determine the base sequence of nucleic acids such as DNA, and the method is considered to be of value for determination of structure of polymeric substances originating from organisms. The determination of structure of such substances likewise requires the visual determination.
Accordingly, autoradiography is a useful method for analysis of the structure and function of tissue of organisms and/or of organism-originating substances, but it has the unfavorable feature that conventional autoradiography requires visual analysis, thereby needing a great amount of time and labor.
Further, the locational information obtained by the analysis of the autoradiograph varies depending on the investigators in charge because of inherent unreliability of visual observation, and the accuracy of the information is limited to a certain extent. Particularly, in such a case that only a small quantity of a sample has been employed, that the intensity of radiation energy emitted by the radioactively labeled substance has been low, or that the exposure has been done under unfavorable conditions, an autoradiographic image visualized on a radiographic film has reduced quality (in regard of sharpness, contrast, etc.) so that satisfactory information can not be obtained and the accuracy is low. These are drawbacks of conventional autoradiography.
In order to improve the accuracy of the locational information, for instance, a visualized autoradiograph can be scanned by means of a device such as a scanning densitometer. However, such scanning process requires increased time and complicated procedures.
In addition to the above-described disadvantages, a sample and radiographic film is required to be placed together in layers for a long period of time to expose the film to a radioactive substance contained in the sample so as to visualize the autoradiograph having the above-mentioned locational information on the radiographic film (several days are usually required). Moreover, the exposure ought to be carried out at a low temperature (0.degree. C. to -90.degree. C.) to avoid appearance of the chemical fog of the photosensitive silver salt in the radiographic film which is caused by various substances contained in the sample. Thus, the exposure ought to be done under specific conditions. Moreover, since the photosensitive silver salt in a radiographic film has a drawback in that it is also sensitive to physical impacts, or is apt to be physically fogged, careful and skillful handling is required. This feature further brings about another complexity in the autoradiographic procedure.
Further, the radiographic film is also exposed to certain natural radioactive substances contained in the sample other than the radioactively labeled substances under analysis during the exposure for a long period of time. Accordingly, this exposure also lowers the quality of the obtained image, in addition to the above-mentioned effects of chemical and physical fogging.